Embryonic lethality and defective mammary gland development of activator‐function impaired conditional knock‐in Erbb3 ( V943R ) mice

ERBB3 is a pseudokinase domain‐containing member of the ERBB family of receptor tyrosine kinases (RTKs). Following ligand binding, ERBB receptors homo‐ or hetero‐dimerize, leading to a head‐to‐tail arrangement of the intracellular kinase domains, where the “receiver” kinase domain of one ERBB is activated by the “activator” domain of the other ERBB in the dimer. In ERBB3, a conserved valine at codon 943 (V943) in the kinase C‐terminal domain has been shown to be important for its function as an “activator” kinase in vitro. Here we report a knock‐in mouse model where we have modified the endogenous Erbb3 allele to allow for tissue‐specific conditional expression of Erbb3 ( V943R ) (Erbb3 ( CKI‐V943R )). Additionally, we generated an Erbb3 ( D850N ) (Erbb3 ( CKI‐D850N )) conditional knock‐in mouse model where the conserved aspartate in the DFG motif of the pseudokinase domain was mutated to abolish any potential residual kinase activity. While Erbb3 ( D850N/D850N ) animals developed normally, homozygous Erbb3 ( V943R/V943R ) expression during development resulted in embryonic lethality. Further, tissue specific expression of Erbb3 ( V943R/V943R ) in the mammary gland epithelium following its activation using MMTV‐Cre resulted in delayed elongation of the ductal network during puberty. Single‐cell RNA‐seq analysis of Erbb3 ( V943R/V943R ) mammary glands showed a reduction in a specific subset of fibrinogen‐producing luminal epithelial cells.